The rectifier (a high-voltage diode) connected to the magnetron that supplies the RF energy that does the heating in the microwave was shorted. The shorted rectifier was found by using a multimeter to measure resistance which should be very high in this type of diode. After replacing the rectifier the Frigidaire microwave oven heated food normally. I thank AppliancePartsPros for sending the part so promptly.
The real problem with this repair was getting this over the stove microwave oven out of the cabinet .I had to research how it was mounted and then with all bolts removed it was stuck in the cabinet.Getting it out and back in was difficult especially for one man.